A fiber communication system may be categorized into single wavelength fiber communication systems and wavelength division multiplexing fiber communication systems according to the number of optical signals used to provide the carried services.
FIG. 1 shows a typical structure of a single wavelength fiber communication system. A transmitter, TX, transmits signal light with the wavelength of λ, and the signal light is input to a fiber amplifier at the transmitting end, which amplifies the power of the signal light. Upon amplification, the signal light is transmitted in a transmission fiber. Because the transmission fiber has signal losses, the signal light transmitted in the transmission fiber is lost gradually. The signal light is then amplified by a fiber amplifier at the receiving end, and received by a receiver, RX.
The wavelength division multiplexing technology is a communication technology in which optical signals of multiple wavelengths are transmitted in a same fiber. FIG. 2 shows a typical structure of a wavelength division multiplexing fiber communication system. As shown in FIG. 2, transmitters TX1, TX2, TX3, . . . , TXn transmit signal lights with wavelengths of λ1, λ2, λ3, . . . , λn, respectively. The signal lights with different wavelengths are coupled by a wavelength division multiplexer and transmitted in a same fiber. The signal light is input to a fiber amplifier, which amplifies the power of the signal light. Upon amplification, the signal light is transmitted in a transmission fiber; because the transmission fiber has signal losses, the signal light transmitted in the transmission fiber is lost gradually. The signal light is then amplified by a next fiber amplifier. This process continues until the signal light with wavelengths of λ1, λ2, λ3, . . . , λn is split and transmitted to different output ports, and received by receivers RX1, RX2, RX3, . . . , RXn.
It can be seen that the fiber amplifier in a fiber communication system amplifies the power of the signal light, compensates the signal loss, and plays the role of a repeater. The fiber amplifier technology has developed rapidly. Fiber amplifiers with different structures and performances are already designed to meet different application requirements. Existing fiber amplifiers include erbium doped fiber amplifier, praseodymium doped fiber amplifier, thulium doped fiber amplifier, and Raman fiber amplifier.
Fiber amplifiers with different structures and performances are composed of gain medium, pump source, and input/output coupling structure. According to different gain media, the existing fiber amplifiers are categorized into two types: one type adopts active media, for example, erbium doped fiber amplifier, and the other type is based on the non-linear effect of the fiber, for example, Raman fiber amplifier.
With the fast development of fiber communication networks, there are increasing demands for the fiber communication equipment, and system operators have higher requirements for the integration of the fiber communication equipment. The fiber amplifier, as an important component of the fiber communication equipment, is developing towards small size and high integration. The existing fiber amplifiers are generally formed by discrete optical components or hybrid low-integrated components under an inline package based on the existing discrete component package technology. Because the integration is based on one dimension, the number of integrated components is generally less than three but no greater than four. Due to limitation of the package form and size of the components, it is difficult to shrink the size of the fiber amplifier.
For example, the erbium doped fiber amplifier (EDFA) adopts an erbium doped fiber (EDF) as the gain medium. Inside the EDFA, an optical connector, an optical splitter, an optical isolator, an optical wavelength multiplexer, an EDF, a gain flattening filter, a pump laser, and an optical detector are connected through fiber splicing. FIG. 3 shows a typical structure of an EDFA optical channel, where adding or removing some components may implement different functions or performances.
The conventional technical solution has the following weaknesses:
1. The fiber amplifier needs multiple active components and passive components. The size of the fiber amplifier is very difficult to reduce due to some factors, such as the large number and size of components, large number of fiber fusion splices and difficulty in fiber winding.
2. The passive components have large losses, and there are many fiber fusion splices. The accumulated losses hinder the optimization of the output power and noise coefficient of the fiber amplifier.
3. Optical passive and active components must undergo a complex package process, requiring high costs.
The fiber amplifier requires a complex production process, long processing duration, and high manufacturing costs.
4. The discrete components are combined.
The optical energy passes through multiple components and there are many optical fusion splices between the components. This may reduce the reliability of the fiber amplifier. In particular, a high power fiber amplifier has strict quality requirements for fiber fusion splices. The failure of fiber fusion spices is a main cause for the failure of the fiber amplifier. Too many fiber fusion splices may directly affect the reliability of the fiber amplifier.